1. Field of the Invention
The present invention relates to a semiconductor light emitting element having an opposed-electrode structure in which a positive electrode and a negative electrode are formed as a pair to sandwich semiconductor layers.
2. Description of the Related Art
Conventionally, in the field of the semiconductor light emitting elements, uniform inplane distribution of light emission is demanded, and therefore uniform current density is required in the gap between the electrodes. For example, for the semiconductor light emitting elements in which a positive electrode (p-electrode) and a negative electrode (n-electrode) are formed as a pair on the same side of a semiconductor layer, techniques for homogenizing the current density by equalizing the distances between the p-electrode and the n-electrode as much as possible have been disclosed, for example, in Japanese Patent Laid-open Nos. 2006-012916, 2001-345480, 2007-116153, and 2004-056109 (which are hereinafter referred to as JP 2006-012916 A, JP 2001-345480 A, JP 2007-116153 A, and JP 2004-056109 A, respectively). (See FIG. 8 in JP 2006-012916 A, FIG. 1 in JP 2001-345480 A, FIG. 2 in JP 2007-116153 A, and FIG. 3 in JP 2004-056109 A.)
Specifically, JP 2006-012916 A proposes a light emitting element having a comb-like electrode arrangement in which a p-electrode region and an n-electrode region extend deep into each other. JP 2001-345480 A proposes a semiconductor light emitting element in which the maximum distance between the p-electrode region and the n-electrode region is 500 micrometers or less.
JP 2007-116153 A proposes a semiconductor light emitting element in which a p-type electrode is sectioned by first and second n-type branch electrodes, and all the sections of the p-type electrode are electrically connected. JP 2004-056109 A proposes a semiconductor light emitting element in which linear n-electrodes are formed on a plurality of portions of an n-type layer exposed through a plurality of slits, and p-electrodes constituted by a p-ohmic electrode and current diffusion conductors are formed adjacent to the linear n-electrodes.
However, in the conventional semiconductor light emitting elements having an opposed-electrode structure in which a positive electrode and a negative electrode are formed as a pair to sandwich semiconductor layers, it has been impossible to homogenize the current density in the gap between the electrodes even if the electrodes are arranged in a similar manner to one of the proposals by JP 2006-012916 A, JP 2001-345480 A, JP 2007-116153 A, and JP 2004-056109 A. The reason for the impossibility of homogenization can be considered as follows. That is, current flows in the thickness direction (surface normal direction) in the semiconductor light emitting elements having the opposed-electrode structure, while current strongly tends to flow in an in-plane direction in the semiconductor light emitting elements in which a positive electrode and a negative electrode are formed as a pair on the same side of a semiconductor layer. Therefore, the current flow and the electrode arrangement which is suitable for the current flow are completely different between the semiconductor light emitting elements having the opposed-electrode structure and the semiconductor light emitting elements in which a positive electrode and a negative electrode are formed on the same side of a semiconductor layer.
Particularly, in the semiconductor light emitting elements proposed by JP 2006-012916 A, JP 2001-345480 A, JP 2007-116153 A, and JP 2004-056109 A, the external connections and the branch points of elongated portions are arranged near the side faces of a semiconductor layer because of necessity to attain the greatest possible light emission area. Further, in the semiconductor light emitting elements proposed by JP 2006-012916 A, JP 2001-345480 A, and JP 2007-116153 A, electrodes are continually arranged near the side faces of semiconductor layers. Therefore, if the electrode arrangement in the semiconductor light emitting elements having the opposed-electrode structure is modified to an arrangement similar to the arrangements proposed by JP 2006-012916 A, JP 2001-345480 A, JP 2007-116153 A, and JP 2004-056109 A, the external connections and the branch points of elongated portions are arranged near the side faces of the semiconductor layers. Since current is likely to concentrate in the regions near the side faces because of the above electrode formation, and is inherently likely to concentrate around the external connections and the branch points of elongated portions, the concentration of current in the regions near the side faces is further enhanced by the above arrangement of the external connections and the branch points of elongated portions, so that the variations in the current density between the central region and the regions near the side faces of the semiconductor layers increase. That is, according to the conventionally proposed techniques, it is impossible to uniform the distribution of light emission in the semiconductor light emitting elements having the opposed-electrode structure.
The present invention has been developed in view of the above circumstances. The object of the present invention is to improve the overall distribution of light emission in a semiconductor light emitting element having the opposed-electrode structure (in which a positive electrode and a negative electrode are formed as a pair to sandwich semiconductor layers) by homogenizing the current density in the gap between the electrodes.